Measuring gauges are a common necessity in many manufacturing processes. In the manufacture of thin wall seamless tubing it is common to use a mill sometimes called a pilger mill which has two relatively thick disk shaped dies. These dies have grooves along the outer periphery of the die which work upon the outer surfaces of the tubing so as to reduce the wall thickness and diameter. A mandrel is usually inserted into the interior of a tube to maintain the inside diameter.
In many applications outside surface finish of tubing is critical and wall thickness and diameter must be maintained to within very close tolerances. In order to produce such exacting tubing it is necessary to have even more exacting groove shapes in the disk shaped dies. Previously, it has been common for small approximately semicircular disk gauges to be placed transversely into the groove and a visual examination is made for light leakage between the gauge and the groove in order to assure that the die is properly shaped and sized for the manufacturing process. Such visual inspection of the die grooves has been found unacceptable in many instances where tubing having very close tolerances must be manufactured. Visual inspection using such a gauge has been able to produce groove dimensions having tolerances within approximately 0.0005 inches.
Another limitation of the prior art involved the need to measure die grooves which were noncircular in cross-sectional shape. Since it is difficult to produce gauges having a noncircular shape, it was even more difficult to use these gauges to produce a properly shaped noncircular groove in the edge of the die.
Prior art gauges have also suffered from the limitation that data could not very easily be produced and stored concerning the interior contour shape of the die grooves. Such information is useful to analyzing the die wear patterns and rates of wear, so that improvements can be made in die design.
Mechanical gauges having the ability to measure interior contours are shown in the prior art but have all suffered from limitations in accuracy because of the various structures used for probing, detecting and transmitting the measurements. The current invention minimizes the amount of measurement error through a number of novel improvements which will be fully described below. Other objectives and features of the invention will also be apparent from the following description.